1. Field of the Invention
The present invention relates to a control circuit, and particularly to a control circuit for providing a backup control for controlling rotational speed of a fan.
2. Description of Related Art
Generally, a computer system includes a motherboard with various chips such as a central processing unit (CPU) mounted thereon, a storage device such as a hard disc, and input/output devices, each of which is known to generate heat when operated in a computer system. Especially, the CPU produces a large amount of heat. Developments in today's information-intensive society have led to remarkable improvements in performances of electronic devices. If the heat generated from the CPU is not dissipated in a timely fashion, it may damage the CPU or even the computer system.
Typically, a sensor is programmed to be used as a temperature detector for detecting temperature of the CPU. A cooling fan is used to facilitate removal of heat to keep the temperature of the CPU within a safe temperature range. The sensor sends a pulse-width modulation (PWM) signal to the cooling fan to adjust fan speed to be more energy efficient while still providing enough heat dissipation. However, the fan will stop operating if the sensor fails, and the CPU may be damaged if the heat is not dissipated properly.
What is desired, therefore, is a control circuit for automatically providing backup control for controlling rotational speed of a fan.